The present invention relates to a method of packaging a beverage. More particularly, the invention concerns the packaging of beverage having gas in solution in a sealed container of the kind which has a primary chamber containing the beverage and which forms a primary headspace comprising gas at a pressure greater than atmospheric; communicating with the primary chamber by way of a restricted orifice is a secondary chamber containing fluid at a pressure greater than atmospheric and which is arranged so that when the container is broached to dispense the beverage, the primary headspace is opened to atmospheric pressure and the pressure differential created by the decrease in pressure in the primary headspace causes fluid in the secondary chamber to be ejected by way of the restricted orifice into the beverage in the primary chamber and that ejection results in gas in solution in the beverage to be evolved and form, or assist in the formation of, a head of froth on the beverage.
An example of a beverage package of the kind discussed is disclosed in our European Patent 0 227 213 and following from that development, these packages have become very well known in the art and have met with considerable commercial success. Our aforementioned European Patent Specification is primarily concerned with the initial ejection of beverage from the secondary chamber, by way of the restricted orifice, into the primary chamber upon opening of the container by the pressure differential which is created between atmospheric pressure in the primary headspace and a secondary headspace which is at a pressure greater than atmospheric in the secondary chamber; the development of a desirable froth or head on the beverage is fully discussed in our European Specification and in the prior art to which it refers. Among that prior art is reference to our British Patent No. 1,266,351 which is directed to the initial ejection of gas from the secondary chamber by way of a restricted orifice into beverage in the primary chamber for the purpose of froth formation. Initial gas ejection from the secondary chamber to the primary chamber is considered, by some, to provide desirable characteristics of froth formation which are preferable to those achieved by initial beverage ejection. Furthermore tests have indicated that by use of intial gas ejection for froth development from the secondary chamber to the primary chamber, it is possible to reduce the pressure within the container when its sealed contents are in equilibrium as compared with such pressure as would be required for initial beverage ejection. The possibility of using relatively low pressure within the sealed container is undoubtedly desirable economically, environmentally and for safety reasons, particularly in a high speed filling line along which successive containers are charged with beverage and sealed to form the package.
Prior attempts to provide beverage packages of the kind discussed in which, upon opening, gas is initially ejected from the secondary chamber, through the restricted orifice and into the primary chamber for the purposes of head formation have met with little success commercially. Principally this was due to the difficulty and costs involved in achieving and maintaining the gas under pressure in the secondary chamber to ensure that such gas, and not beverage, was initially ejected through the restricted orifice and into the beverage in the primary chamber for froth development. As far as we are aware, attempts to achieve initial gas ejection have necessitated in the secondary chamber in the form of a hollow insert being charged and sealed with nitrogen gas under pressure remotely from the container and provided with a non-return valve associated with the restricted orifice. The sealed insert is placed in a container which is charged with beverage and itself sealed with the beverage under pressure. The beverage package is subsequently heated during pasteurisation causing the insert to deform so that the non-return valve becomes operative and responsive to the pressure differential previously mentioned whereby it permits the required initial gas ejection from the insert whilst preventing beverage from the primary chamber entering the secondary chamber of the insert. This remote nitrogen gas charging and sealing of the secondary chamber in the insert and the provision of a non-return valve in the structure of the insert require expensive manufacture and processing stages. In particular it is believed that the necessity for the insert to be subjected to heat deformation for its operational characteristics to become effective requires unreasonably expensive manufacturing costs for a reliable structure of the gas charged and sealed insert. Also the remote gas charging and sealing of the insert where the latter is of plastics can result in atmospheric oxygen migrating through the walls of the insert and into the secondary chamber to contaminate the nitrogen gas during the intervening period between the sealing of the insert and the sealing of the insert in the container. In the prior proposal of the gas filled and sealed insert, it has also been found necessary for the pressure in the primary chamber to exceed that in the secondary chamber to a considerable extent to ensure that the insert retains its foam initiation potential in the sealed container following the deformation of the insert by heating; further expense is therefore incurred in ensuring that adequate pressurisation is provided in the headspace of the sealed container. Even so it is also found that when the container is opened for consumption of the beverage and following gas ejection from the insert, a considerable charge of gas and residual pressure can be retained in the insert by the non-return valve--this may cause a relatively violent discharge if the insert is pierced or otherwise tampered with. It is an object of the present invention to provide a method of packaging a beverage to form a beverage package of the kind discussed in which upon opening of the package gas is initially ejected from the secondary chamber and by way of the restricted orifice into beverage in the primary chamber for the purposes of froth or head development and which method alleviates the disadvantages of the prior proposals.